Field of the Invention
The present invention relates to a solid electrolytic capacitor including a conductive polymer material as solid electrolyte. The present invention more specifically relates to a solid electrolytic capacitor having a reduced leakage current and well sustaining the effect of the reduced leakage current even after long-term use of the capacitor at high temperatures.
Description of the Related Art
Typical electrolytic capacitors including an electrolyte solution as electrolyte can repair defects generated in dielectric oxide films during production of the capacitors. For this reason, the leakage current is not significantly increased. In contrast, solid electrolytic capacitors including a solid electrolyte as electrolyte cannot repair the dielectric oxide film because the electrolytes are solids. Thus, solid electrolytic capacitors cannot self-repair defects generated in the dielectric oxide film. Accordingly, if the dielectric oxide films are degraded by mechanical stress or thermal stress during production, the solid electrolytic capacitors tend to have significantly increased a leakage current. The solid electrolytic capacitors in the related art have been aged to reduce the leakage current due to the solid electrolytes. In this aging treatment, the dielectric oxide films are repaired with the moisture content absorbed from the atmosphere. The aging treatment depends on the moisture absorbing properties of the device.
For this problem, JP2001-196271A (D1) proposes a solid electrolytic capacitor including a capacitor element including a valve metal, an oxide film layer formed on the surface of the valve metal, and a solid electrolyte layer formed on the oxide film layer, and an exterior accommodating the capacitor element, wherein the capacitor element contains an organic compound having a boiling point of 150° C. or more and a melting point of 150° C. or less. In D1, the organic compound has a boiling point of more preferably 200° C. or more, particularly preferably 250° C. or more.
JP2014-045115A (D2) proposes a solid electrolytic capacitor including a solid electrolyte layer and an oxide film repairing layer composed of a gelated layer retaining moisture. The oxide film repairing layer can function as follows: If a leakage current (LC) flows into defects of a dielectric layer, the LC reaches the oxide film repairing layer and electrically decomposes water retained in the oxide film repairing layer to generate oxygen. The generated oxygen is fed to the valve metal corresponding to the defects to form a stable oxide film.
Unfortunately, the leakage current is still large in the configuration of D1. After long-term use of the solid electrolytic capacitor at high temperatures, it is difficult to completely prevent volatilization of the organic compound used even if the organic compound has a high boiling point. As a result, the effect of repairing the oxide film reduces with a reduction in the organic compound, and an increase in LC cannot be prevented.
In D2, although the oxide film repairing layer composed of a gelled layer retaining water is a solidified gel, water gradually volatilizes under high temperatures to reduce the ability to repair the oxide film. In other words, the durability at high temperatures of the solid electrolytic capacitor still has room for improvement. Moreover, the configuration of the oxide film repairing layer disposed between the oxide film and the solid electrolyte layer readily increases equivalent series resistance (ESR).